Semaphorin 4D (SEMA4D), also known as CD100, is a transmembrane protein (e.g., SEQ ID NO: 1 (human); SEQ ID NO: 2 (murine)) that belongs to the class IV semaphorin gene family. SEMA4D is expressed on the cell surface as a homodimer, but upon cell activation SEMA4D can be released from the cell surface via proteolytic cleavage to generate sSEMA4D, a soluble form of the protein, which is also biologically active. See Suzuki et al., Nature Rev. Immunol. 3:159-167 (2003); Kikutani et al., Nature Immunol. 9:17-23 (2008).
SEMA4D is expressed at high levels in lymphoid organs, including the spleen, thymus, and lymph nodes, and in non-lymphoid organs, such as the brain, heart, and kidney. In lymphoid organs, SEMA4D is abundantly expressed on resting T cells but only weakly expressed on resting B cells and antigen-presenting cells (APCs), such as dendritic cells (DCs). Its expression, however, is upregulated in these cells following activation by various immunological stimuli. The release of soluble SEMA4D from immune cells is also increased by cell activation.
Atherosclerosis has been recognized as an inflammatory disease in which the immune cells play crucial roles during disease progression (Hansson G K et al., Nat Rev Immunol 6: 508-519, 2006). Macrophages express CD40 molecules and T cells have CD40 ligand (CD40L or CD154) on their cell surfaces (Mach F et al., Circulation 96: 396-399, 1997; and Mach F et al., Proc Natl Acad Sci USA 94: 1931-36, 1997). CD40 ligation with CD40L on intraplaque immune cells induces the secretion of proteases and pro-inflammatory mediators, which expands inflammatory activation (Mach F et al., Circulation 96: 396-399, 1997). Blockade of CD40 ligation or a CD40L gene knockout can retard atherosclerotic plaque development in atherosclerosis-prone mice (Mach F et al., Nature 394: 200-203, 1998; and Lutgens E et al., Nat Med 11: 1313-1316, 1999). CD40 ligation on immune cells with stimulating anti-CD40 antibodies has been reported to induce the expression of Sema4D (CD100) (Kumanogoh A et al., Immunity 13: 621-31, 2000).
SEMA4D has been implicated in various processes such as enhancing the immune response, angiogenesis, epithelial morphogenesis and bone remodeling (Kruger R P et al., Nat Rev Mol Cell Biol 6: 789-800, 2005; Pasterkamp R. J., Nat Rev Neurosci 13:605-618, 2012; and Kang S et al., Seminars in Cell & Dev Biol 24:163-171, 2013). Lymphocytes, macrophages, endothelial cells and platelets in atherosclerotic plaques express plexin-B1 on their membrane surface, a high affinity receptor for Sema4D (Basile J R et al., Moll Cell Biol 25: 6889-6898, 2005; Delaire S et al., J Immunol 166: 4348-4354, 2001; and Chabbert-de Ponnat I et al., Int Immunol 17: 439-447, 2005). Sema4D expressed by T cells or released from the T cell membrane can, therefore, have certain effects on cells located in atherosclerotic plaques (Basile J R et al., Mol. Cell Biol 25: 6889-6898, 2005; Delaire S et al., J Immunol 166: 4348-4354, 2001; and Chabbert-de Ponnat I et al., Int Immunol 17: 439-447, 2005). Previous studies revealed pro-angiogenic activity of Sema4D on endothelial cells in vitro and in vivo (Conrotto P et al., Blood 105: 4321-4329, 2005; and Basil J R et al., Cancer Res 64: 5212-5224, 2004.). Moreover, high level of expression of Sema4D was observed in several squamous cell carcinomas suggesting a critical role of Sema4D in tumor-induced angiogenesis in vivo (Basile J R et al., Proc Natl Acad Sci USA 103: 9017-9022, 2006.). Thus, Sema4D can affect plaque growth by, e.g., promoting the neovascularization process occurring in atheroma. In fact, one study revealed that deleting the Sema4D gene in atherosclerosis-prone ApoE deficient (ApoE−/−) mice delayed the growth of atherosclerotic plaques and neovascularization in the plaque area, suggesting that blocking the Sema4D signal during the progression phase of atherosclerosis can prevent the plaque growth and neovascularization (Yukawa K et al., Int. J Mol. Med. 26: 39-44, 2010).